U.S. patent application number 15/738735 was filed with the patent office on 2018-07-05 for tube glass cutting method and cutting device, and tube glass product manufacturing method.
The applicant listed for this patent is Nippon Electric Glass Co., Ltd.. Invention is credited to Masato INOUE, Masanori WADA.
Application Number | 20180186679 15/738735 |
Document ID | / |
Family ID | 57760850 |
Filed Date | 2018-07-05 |
United States Patent
Application |
20180186679 |
Kind Code |
A1 |
WADA; Masanori ; et
al. |
July 5, 2018 |
TUBE GLASS CUTTING METHOD AND CUTTING DEVICE, AND TUBE GLASS
PRODUCT MANUFACTURING METHOD
Abstract
With a method of cutting a tube glass (G1) according to the
present invention, the tube glass (G1) is irradiated with laser
light (L) having a focal point (F) adjusted to an inside of the
tube glass (G1), to thereby form an inner crack region (C1)
including one or more cracks in a portion of the tube glass (G1) in
a circumferential direction of the tube glass (G1) through
multiphoton absorption that occurs in an irradiation region of the
laser light (L). Then, in the tube glass (G1), there is generated a
stress that urges the one or more cracks in the inner crack region
(C1) to propagate in the circumferential direction of the tube
glass (G1) to cause the one or more cracks to propagate throughout
an entire circumference of the tube glass (G1), to thereby cut the
tube glass (G1).
Inventors: |
WADA; Masanori; (Shiga,
JP) ; INOUE; Masato; (Shiga, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nippon Electric Glass Co., Ltd. |
Shiga |
|
JP |
|
|
Family ID: |
57760850 |
Appl. No.: |
15/738735 |
Filed: |
March 30, 2016 |
PCT Filed: |
March 30, 2016 |
PCT NO: |
PCT/JP2016/060308 |
371 Date: |
December 21, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 26/53 20151001;
C03B 33/0222 20130101; C03B 33/0955 20130101; B23K 2101/06
20180801; B23K 26/38 20130101; C03B 33/06 20130101; B23K 2103/54
20180801; B28D 1/221 20130101; Y02P 40/57 20151101; B23K 26/0846
20130101 |
International
Class: |
C03B 33/095 20060101
C03B033/095; B23K 26/38 20060101 B23K026/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2015 |
JP |
2015-127831 |
Dec 17, 2015 |
JP |
2015-246329 |
Claims
1. A method of cutting a tube glass, comprising: irradiating the
tube glass with laser light having a focal point adjusted to an
inside of the tube glass, to thereby form an inner crack region
including one or more cracks in a portion of the tube glass in a
circumferential direction of the tube glass through multiphoton
absorption that occurs in an irradiation region of the laser light;
and generating, in the tube glass, a stress that urges the one or
more cracks in the inner crack region to propagate in the
circumferential direction of the tube glass to cause the one or
more cracks to propagate throughout an entire circumference of the
tube glass, to thereby cut the tube glass.
2. The method of cutting a tube glass according to claim 1,
comprising forming the inner crack region on an outer periphery
side of the tube glass in a thickness direction of the tube
glass.
3. The method of cutting a tube glass according to claim 1,
comprising forming the inner crack region into an arc shape in
conformity with the tube glass.
4. The method of cutting a tube glass according to claim 1,
comprising causing the laser light to perform scanning so that the
focal point is included in an imaginary cross section orthogonal to
a center line of the tube glass.
5. The method of cutting a tube glass according to claim 1,
comprising dispersing the laser light and irradiating a plurality
of points of the inside of the tube glass with the dispersed laser
light so that each focal point is included in an imaginary cross
section orthogonal to a center line of the tube glass.
6. The method of cutting a tube glass according to claim 1,
comprising: forming the inner crack region in a vicinity of an
outer peripheral surface of the tube glass by irradiation with the
laser light while leaving a surface layer portion including the
outer peripheral surface; causing the one or more cracks in the
inner crack region to propagate to the outer peripheral surface;
and causing the one or more cracks to propagate throughout the
entire circumference of the tube glass with a stress that urges the
one or more cracks to propagate in the circumferential direction of
the tube glass.
7. The method of cutting a tube glass according to claim 6,
comprising generating abrasion in the surface layer portion to form
a plurality of holes extending in an irradiation direction of the
laser light by irradiation with the laser light, and adjusting a
circumferential interval between the plurality of holes, to thereby
cause the one or more cracks in the inner crack region to propagate
to the outer peripheral surface so as to connect the plurality of
holes to each other.
8. The method of cutting a tube glass according to claim 7,
comprising setting a circumferential pitch between the plurality of
holes to 1.5 times or more and 5.0 times or less an inner diameter
of the holes.
9. The method of cutting a tube glass according to claim 6,
comprising setting a thickness of the surface layer portion to 20
.mu.m or less.
10. The method of cutting a tube glass according to claim 1,
comprising irradiating the tube glass with the laser light having a
focal point adjusted to an inside of the tube glass under a state
of generating, in the tube glass, a stress that urges the one or
more cracks in the inner crack region to propagate in the
circumferential direction of the tube glass, to thereby form the
inner crack region in the portion of the tube glass in the
circumferential direction.
11. The method of cutting a tube glass according to claim 1,
comprising applying a tensile force to the tube glass in a
direction along a longitudinal direction of the tube glass, to
thereby generate the stress that urges the one or more cracks to
propagate in the circumferential direction of the tube glass.
12. The method of cutting a tube glass according to claim 1,
comprising applying a bending force to the tube glass so that the
center line of the tube glass is curved with a predetermined
curvature, to thereby generate the stress that urges the one or
more cracks to propagate in the circumferential direction of the
tube glass.
13. The method of cutting a tube glass according to claim 1,
comprising subjecting a portion of the tube glass in which the
inner crack region is formed to local heating and cooling, to
thereby generate the stress that urges the one or more cracks to
propagate in the circumferential direction of the tube glass.
14. An cutting device for a tube glass, comprising: an inner crack
region forming device configured to irradiate the tube glass with
laser light having a focal point adjusted to an inside of the tube
glass, thereby being capable of forming an inner crack region
including one or more cracks in a portion of the tube glass in a
circumferential direction of the tube glass through multiphoton
absorption that occurs in an irradiation region of the laser light;
and a crack propagation device configured to generate, in the tube
glass, a stress that urges the one or more cracks in the inner
crack region to propagate in the circumferential direction of the
tube glass, to thereby cause the one or more cracks to propagate
throughout an entire circumference of the tube glass.
15. A method of manufacturing a tube glass, comprising cutting a
continuous tube glass subjected to tube drawing forming in a
cutting step provided during conveyance of the continuous tube
glass to provide a tube glass product, the method comprising:
irradiating the continuous tube glass with laser light having a
focal point adjusted to an inside of the tube glass, to thereby
form an inner crack region including one or more cracks in a
portion of the continuous tube glass in a circumferential direction
of the tube glass through multiphoton absorption that occurs in an
irradiation region of the laser light; and generating, in the
continuous tube glass, a stress that urges the one or more cracks
in the inner crack region to propagate in the circumferential
direction of the continuous tube glass to cause the one or more
cracks to propagate throughout an entire circumference of the
continuous tube glass, to thereby cut the continuous tube glass to
provide a tube glass product.
16. The method of cutting a tube glass according to claim 2,
comprising forming the inner crack region into an arc shape in
conformity with the tube glass.
17. The method of cutting a tube glass according to claim 2,
comprising causing the laser light to perform scanning so that the
focal point is included in an imaginary cross section orthogonal to
a center line of the tube glass.
18. The method of cutting a tube glass according to claim 3,
comprising causing the laser light to perform scanning so that the
focal point is included in an imaginary cross section orthogonal to
a center line of the tube glass.
19. The method of cutting a tube glass according to claim 16,
comprising causing the laser light to perform scanning so that the
focal point is included in an imaginary cross section orthogonal to
a center line of the tube glass.
20. The method of cutting a tube glass according to claim 2,
comprising dispersing the laser light and irradiating a plurality
of points of the inside of the tube glass with the dispersed laser
light so that each focal point is included in an imaginary cross
section orthogonal to a center line of the tube glass.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of cutting a tube
glass and a cutting device for a tube glass, and a method of
manufacturing a tube glass product.
BACKGROUND ART
[0002] A tube glass product used in, for example, a medical ampule
and a fluorescent tube for lighting is formed by various methods
such as a Danner method and a down-draw method. The overview of the
Danner method is described below as an example.
[0003] When a tube glass product is manufactured by the Danner
method, a molten glass is first supplied to a rotatable sleeve
arranged in a muffle furnace. The supplied molten glass is formed
into a tube shape while being wound on an inside of the sleeve.
Then, the molten glass formed into a tube shape is pulled out from
a distal end of the sleeve with a tube drawing device (pulling
device) to form a tube glass continuously. After that, the formed
tube glass (continuous tube glass) is cut to a predetermined length
with a cutting device to obtain a tube glass product having a
predetermined length (see, for example, Patent Literature 1).
[0004] Further, in this case, as a method of cutting the continuous
tube glass, there has been generally adopted a method involving
bringing a cutting blade into contact with an outer peripheral
surface of the continuous tube glass that is conveyed continuously
to form scratches on the outer peripheral surface, and applying
thermal shock to the scratches, to thereby cut the continuous tube
glass (see, for example, Patent Literature 2).
CITATION LIST
[0005] Patent Literature 1: JP 2013-159532 A
[0006] Patent Literature 2: JP 2013-129546 A
SUMMARY OF INVENTION
Technical Problem
[0007] The method described in Patent Literature 2 enables the
continuous tube glass to be cut while being conveyed. Therefore,
the method described in Patent Literature 2 is excellent in that
the continuous tube glass can be cut at a relatively high speed,
and the method can be easily incorporated into a manufacturing
line. However, in the method involving forming scratches on the
outer peripheral surface of the continuous tube glass and causing
the scratches to propagate through thermal shock as described
above, it is difficult to stabilize the shape of the scratches
serving as a starting point of cracks, and hence a fracture surface
(cut surface) is rough, with the result that the fracture surface
is finished with unsatisfactory quality. Further, cutting
processing for finishing the fracture surface in a flat shape is
additionally required, resulting in an increase in number of
processes. Further, in the method involving forming scratches on
the outer peripheral surface of the tube glass, glass powder is
inevitably generated, and hence the step of cleaning the glass
powder adhering to the inner peripheral surface of the tube glass
after being cut is also separately required.
[0008] In view of the above-mentioned circumstances, in this
description, a first technical object to be achieved by the present
invention is to provide a method of cutting a tube glass and a
cutting device for a tube glass, which enable satisfactory quality
of a cut surface and are capable of preventing generation of glass
powder in spite of cutting the tube glass at a high speed.
[0009] Further, in view of the above-mentioned circumstances, in
this description, a second technical object to be achieved by the
present invention is to provide a method of manufacturing a tube
glass product, which enables satisfactory quality of a cut surface
and is capable of preventing generation of glass powder in spite of
cutting the tube glass at a high speed.
Solution to Problem
[0010] The first technical object is achieved by a method of
cutting a tube glass according to the present invention. That is,
the method of cutting a tube glass comprises: irradiating the tube
glass with laser light having a focal point adjusted to an inside
of the tube glass, to thereby form an inner crack region including
one or more cracks in a portion of the tube glass in a
circumferential direction of the tube glass through multiphoton
absorption that occurs in an irradiation region of the laser light;
and generating, in the tube glass, a stress that urges the one or
more cracks in the inner crack region to propagate in the
circumferential direction of the tube glass to cause the one or
more cracks to propagate throughout an entire circumference of the
tube glass, to thereby cut the tube glass.
[0011] In the present invention, the inner crack region is formed
in the tube glass through multiphoton absorption that occurs at a
time of irradiation with laser light, and the cracks in the inner
crack region are caused to propagate to cut the tube glass.
Therefore, the situation in which glass powder similar to scratches
is generated during formation of an initial crack (crack in the
inner crack region) can be avoided. Therefore, the time and labor
for removing the glass powder by cleaning can be omitted to reduce
the number of required processes. Further, in the present
invention, the stress that urges the cracks in the inner crack
region to propagate in the circumferential direction of the tube
glass is generated in the tube glass, to thereby cause the cracks
to propagate throughout the entire circumference of the tube glass.
Therefore, an entire region of a cut surface can be formed of
fracture surfaces of the cracks in the inner crack region formed
through multiphoton absorption of the laser light and fracture
surfaces of the cracks that propagate from the inner crack region.
When the cut surface is formed as described above, as compared to
the case in which cracks are forcibly generated and caused to
propagate by cleaving or the like, the occurrence of cracking,
chipping, and the like can be prevented to the extent possible to
control the properties of the cut surface with relatively high
precision, with the result that the cut surface with satisfactory
properties can be obtained stably. Further, as described above,
when the inner crack region is formed in the portion of the tube
glass in the circumferential direction thereof with the laser
light, and the cracks in the inner crack region are caused to
propagate in the circumferential direction of the tube glass, a
time period required for cutting becomes shorter as compared to the
case in which the inner crack region is formed throughout an entire
circumference by irradiation with laser light. Accordingly, the
tube glass can be cut at a high speed, and the cutting method
according to the present invention can be easily introduced into,
for example, a manufacturing line.
[0012] Further, with the method of cutting a tube glass according
to the present invention, the inner crack region may be formed on
an outer periphery side of the tube glass in a thickness direction
of the tube glass.
[0013] Further, with the method of cutting a tube glass according
to the present invention, the inner crack region may be formed into
an arc shape in conformity with the tube glass.
[0014] As described above, the cutting method according to the
present invention involves forming the inner crack region through
multiphoton absorption in the irradiation region of the laser
light, and hence the forming position and shape of the inner crack
region can be relatively freely set. In view of the foregoing, the
inventors of the present invention have made investigations on the
preferred forming position or shape of the inner crack region, and
as a result, have found that the cracks are caused to propagate
smoothly and accurately by forming the inner crack region on the
outer periphery side of the tube glass in the thickness direction
thereof at least under predetermined conditions. Alternatively, it
has been found that, even when the inner crack region is formed
into the arc shape in conformity with the tube glass, the
subsequent propagation of the cracks can also be performed smoothly
and accurately. Thus, when the inner crack region is formed so as
to satisfy at least one of the above-mentioned position or shape, a
pair of cracks having propagated in directions separated from each
other in the circumferential direction from the inner crack region
reach a common position at a time when the cracks propagate by the
same distance. Accordingly, the cut surface with significantly
satisfactory properties can be obtained.
[0015] Further, with the method of cutting a tube glass according
to the present invention, the laser light may be caused to perform
scanning so that the focal point is included in an imaginary cross
section orthogonal to a center line of the tube glass.
[0016] When the laser light is caused to perform scanning as
described above, the laser light can be caused to perform scanning
in synchronization with the movement of the tube glass even under a
state in which the tube glass is conveyed. Thus, the tube glass can
be irradiated with the laser light while the focal point is moved
accurately along the circumferential direction of the tube glass,
with the result that the inner crack region can be formed with good
precision in the portion of the tube glass in the circumferential
direction.
[0017] Further, with the method of cutting a tube glass according
to the present invention, the laser light may be dispersed and
irradiated to a plurality of points of the inside of the tube glass
so that each focal point is included in an imaginary cross section
orthogonal to a center line of the tube glass.
[0018] When the laser light is dispersed and irradiated to the
plurality of points of the inside of the tube glass as described
above, the plurality of points of the inside of the tube glass can
be simultaneously irradiated with the laser light. Therefore, in
particular, when the tube glass is conveyed, the plurality of
points can be irradiated with the laser light within a time period
of one laser light irradiation even without performing scanning
with the laser light in consideration of the conveyance speed of
the tube glass (in synchronization with the tube glass), with the
result that the inner crack region can be formed within a short
time period.
[0019] Further, with the method of cutting a tube glass according
to the present invention, the inner crack region may be formed in a
vicinity of an outer peripheral surface of the tube glass by
irradiation with the laser light while a surface layer portion
including the outer peripheral surface is left, and the one or more
cracks in the inner crack region may be caused to propagate to the
outer peripheral surface. Then, the one or more cracks may be
caused to propagate throughout the entire circumference of the tube
glass with a stress that urges the one or more cracks to propagate
in the circumferential direction of the tube glass.
[0020] The inventors of the present invention have found that, when
the inner crack region is formed in the vicinity of the outer
peripheral surface of the tube glass by irradiation with laser
light while the surface layer portion including the outer
peripheral surface is left, the cracks in the inner crack region
propagate to the outer peripheral surface of the tube glass during
formation of the inner crack region depending on the forming
condition of the inner crack region. Further, the inventors of the
present invention have found that, when the cracks propagate to the
outer peripheral surface as described above, the stress required
for subsequent cutting of the entire circumference of the tube
glass may be small. Thus, the cut surface with even more
satisfactory properties can be obtained by, as described above,
adjusting the forming position of the inner crack region to cause
the cracks in the inner crack region to propagate to the outer
peripheral surface and causing the cracks to propagate throughout
the entire circumference of the tube glass with the stress that
urges the cracks to propagate in the circumferential direction of
the tube glass. Needless to say, the cracks generated on the outer
peripheral surface of the tube glass are the cracks in the inner
crack region formed in the tube glass by irradiation with laser
light, which propagate to the outer peripheral surface. Therefore,
there is no risk in that at least glass powder, which may cause a
problem, is not generated.
[0021] Further, in this case, with the method of cutting a tube
glass according the present invention, abrasion may be generated in
the surface layer portion to form a plurality of holes extending in
an irradiation direction of the laser light by irradiation with the
laser light, and a circumferential interval may be adjusted between
the plurality of holes, to thereby cause the one or more cracks in
the inner crack region to propagate to the outer peripheral surface
so as to connect the plurality of holes to each other.
[0022] According to the further investigations by the inventors of
the present invention, the following has been found. The
propagation phenomenon of the cracks in the inner crack region
toward the outer peripheral surface is caused to occur stably (with
significantly high probability) by generating abrasion in the
surface layer portion, in which the inner crack region is not
formed, to form the plurality of holes and adjusting the
circumferential interval between the plurality of holes, when the
cracks in the inner crack region is caused to propagate to the
outer peripheral surface of the tube glass by irradiation with
laser light, as described above. Thus, the cut surface with
satisfactory and stable properties can be obtained by forming the
inner crack region in the tube glass, forming the plurality of
holes through abrasion in the surface layer portion of the tube
glass, in which the inner crack region is not formed, and adjusting
the circumferential interval between the plurality of holes to an
appropriate size.
[0023] Further, with the method of cutting a tube glass according
the present invention, a circumferential pitch between the
plurality of holes may be set so as to be 1.5 times or more and 5.0
times or less an inner diameter of the holes.
[0024] In adjustment of the circumferential interval between the
plurality of holes formed in the surface layer portion through
abrasion to an appropriate size as described above, for example, it
is conceivable that the circumferential pitch between the plurality
of holes be set within an appropriate range in relation to the
inner diameter of the holes. In this case, when the circumferential
pitch between the plurality of holes is set within the
above-mentioned range at a magnification with respect to the inner
diameter of the holes, the cracks propagate smoothly and accurately
so as to connect the plurality of holes adjacent to each other in
the circumferential direction. Thus, the cracks in the inner crack
region can be caused to accurately propagate to the outer
peripheral surface of the tube glass, and the cut surface with
satisfactory and stable properties can be obtained.
[0025] Further, with the method of cutting a tube glass according
to the present invention, a thickness of the surface layer portion
may be set so as to be 20 .mu.m or less.
[0026] The cracks in the inner crack region is caused to propagate
smoothly and accurately toward the outer peripheral surface also by
setting the thickness of the surface layer portion in which the
inner crack region is not formed to a predetermined size or less,
in other words, by appropriately determining the forming range
(depth direction position from the outer peripheral surface) of the
inner crack region. Thus, the cracks in the inner crack region can
be caused to accurately propagate to the outer peripheral surface
of the tube glass, and the cut surface with satisfactory and stable
properties can be obtained.
[0027] Further, with the method of cutting a tube glass according
to the present invention, the tube glass may be irradiated with the
laser light having a focal point adjusted to an inside of the tube
glass under a state of generating, in the tube glass, a stress that
urges the one or more cracks in the inner crack region to propagate
in the circumferential direction of the tube glass, to thereby form
the inner crack region in the portion of the tube glass in the
circumferential direction.
[0028] When the stress that can urge the cracks to propagate is
generated in advance in the tube glass as described above, a stress
distribution state that occurs in the tube glass can be more
accurately reproduced as compared to, for example, the case in
which the above-mentioned stress is generated immediately after the
formation of the inner crack region. Further, the state in which
the stress is generated is maintained more easily when the stress
is generated in the tube glass by applying an external force or the
like to the tube glass in advance. Thus, the cracks are caused to
propagate accurately along a desired direction (circumferential
direction of the tube glass), thereby being capable of stably
providing the more satisfactory cut surface.
[0029] Further, with the method of cutting a tube glass according
to the present invention, a tensile force may be applied to the
tube glass in a direction along a longitudinal direction of the
tube glass, to thereby generate the stress that urges the one or
more cracks to propagate in the circumferential direction of the
tube glass.
[0030] When the tensile force is applied to the tube glass along
the longitudinal direction thereof as described above, the large
tensile stress can be generated in a direction orthogonal to the
inner crack region. Thus, it becomes easy to cause the cracks in
the inner crack region to propagate in the direction orthogonal to
the tensile stress, that is, along the circumferential direction of
the tube glass.
[0031] Further, with the method of cutting a tube glass according
to the present invention, a bending force may be applied to the
tube glass so that the center line of the tube glass is curved with
a predetermined curvature, to thereby generate the stress that
urges the one or more cracks to propagate in the circumferential
direction of the tube glass.
[0032] When the bending force is applied to the tube glass as
described above, the tensile stress among the bending stress
becomes dominant in the inner crack region, in particular, when the
inner crack region is formed on a large-diameter side (outer
periphery side in the thickness direction) under a state in which
the tube glass is bent. Thus, the cracks are allowed to propagate
in the circumferential direction more effectively. Further, in this
case, when the tensile force is applied to the tube glass along the
longitudinal direction together with the bending force, the tensile
force acts in directions, in which one tube glass and the other
tube glass opposed to each other with the cracks interposed
therebetween are separated from each other, when the cracks reach a
radially inner side of the tube glass. Thus, the interference
between the tube glasses on the radially inner side in a curved
state can be avoided to the extent possible to stably provide the
cut surface with satisfactory properties.
[0033] Further, with the method of cutting a tube glass according
to the present invention, a portion of the tube glass in which the
inner crack region is formed may be subjected to local heating and
cooling, to thereby generate the stress that urges the one or more
cracks to propagate in the circumferential direction of the tube
glass.
[0034] According to the above-mentioned method, a desired stress
distribution can be generated with more satisfactory precision as
compared to the case in which an external force (for example, a
tensile force and a bending force) is applied, by accurately
controlling a heating region and a cooling region, and a heating
temperature and a cooling temperature, respectively. Thus, the
higher-quality cut surface can be obtained.
[0035] Further, the first technical object is achieved by a cutting
device for a tube glass according to the present invention. That
is, the cutting device for a tube glass comprises: an inner crack
region forming device configured to irradiate the tube glass with
laser light having a focal point adjusted to an inside of the tube
glass, thereby being capable of forming an inner crack region
including one or more one or more cracks in a portion of the tube
glass in a circumferential direction of the tube glass through
multiphoton absorption that occurs in an irradiation region of the
laser light; and a crack propagation device configured to generate,
in the tube glass, a stress that urges the one or more cracks in
the inner crack region to propagate in the circumferential
direction of the tube glass, to thereby cause the one or more
cracks to propagate throughout an entire circumference of the tube
glass.
[0036] As described above, with the cutting device for a tube glass
according to the present invention, the cracks (inner crack region)
can be formed in the tube glass instead of being formed on the
surface thereof in the same manner as in the method of cutting a
tube glass. Therefore, the situation in which glass powder similar
to scratches is generated can be avoided during formation of the
cracks. Therefore, the time and labor for removing the glass powder
by cleaning can be omitted to reduce the number of required
processes. Further, in the present invention, the stress that urges
the cracks in the inner crack region to propagate in the
circumferential direction of the tube glass is generated in the
tube glass, to thereby cause the cracks to propagate throughout the
entire circumference of the tube glass. Therefore, the entire
region of the cut surface can be formed of fracture surfaces of the
cracks in the inner crack region formed through multiphoton
absorption of the laser light and the fracture surfaces of the
cracks that propagate from the inner crack region. When the cut
surface is formed as described above, as compared to the case in
which the cracks are forcibly generated and caused to propagate by
cleaving or the like, the occurrence of cracking, chipping, and the
like can be prevented to the extent possible to control the
properties of the cut surface with relatively high precision, with
the result that the cut surface with satisfactory properties can be
obtained stably. Further, as described above, when the inner crack
region is formed in the portion of the tube glass in the
circumferential direction thereof with the laser light, and the
cracks in the inner crack region are caused to propagate in the
circumferential direction of the tube glass, the time period
required for cutting becomes shorter as compared to the case in
which the inner crack region is formed throughout the entire
circumference by irradiation with laser light. Accordingly, the
tube glass can be cut at a high speed, and the cutting method
according to the present invention can be easily introduced into,
for example, a manufacturing line.
[0037] Further, the second technical object is achieved by a method
of manufacturing a tube glass according to the present invention.
That is, the method of manufacturing a tube glass comprises cutting
a continuous tube glass subjected to tube drawing forming in a
cutting step provided during conveyance of the continuous tube
glass to provide a tube glass product. The method of manufacturing
a tube glass comprises: irradiating the continuous tube glass with
laser light having a focal point adjusted to an inside of the tube
glass, to thereby form an inner crack region including one or more
cracks in a portion of the continuous tube glass in a
circumferential direction of the tube glass through multiphoton
absorption that occurs in an irradiation region of the laser light;
and generating, in the continuous tube glass, a stress that urges
the one or more cracks in the inner crack region to propagate in
the circumferential direction of the continuous tube glass to cause
the one or more cracks to propagate throughout an entire
circumference of the continuous tube glass, to thereby cut the
continuous tube glass to provide a tube glass product.
[0038] As described above, with the method of manufacturing a tube
glass according to the present invention, the one or more cracks
(inner crack region) can be formed in the continuous tube glass
instead of being formed on the surface of the continuous tube glass
in the same manner as in the method of cutting a tube glass.
Therefore, the situation in which glass powder similar to scratches
is generated can be avoided during formation of the cracks.
Therefore, the time and labor for removing the glass powder by
cleaning can be omitted to reduce the number of required processes.
Further, in the present invention, the stress that urges the cracks
in the inner crack region to propagate in the circumferential
direction of the continuous tube glass is generated in the
continuous tube glass, to thereby cause the cracks to propagate
throughout the entire circumference of the continuous tube glass.
Therefore, the entire region of the cut surface can be formed of
fracture surfaces of the cracks in the inner crack region formed
through multiphoton absorption of the laser light and fracture
surfaces of the cracks that propagate from the inner crack region.
When the cut surface is formed as described above, as compared to
the case in which cracks are forcibly generated and caused to
propagate by cleaving or the like, the occurrence of cracking,
chipping, and the like can be prevented to the extent possible to
control the properties of the cut surface with relatively high
precision, with the result that the cut surface with satisfactory
properties can be obtained stably. Further, as described above,
when the inner crack region is formed in the portion of the
continuous tube glass in the circumferential direction thereof with
the laser light, and the cracks in the inner crack region are
caused to propagate in the circumferential direction of the
continuous tube glass, the time period required for cutting becomes
shorter as compared to the case in which the inner crack region is
formed throughout the entire circumference by irradiation with
laser light. Accordingly, the continuous tube glass can be cut at a
high speed, and the manufacturing speed can be increased.
Advantageous Effects of Invention
[0039] As described above, with the method of cutting a tube glass
and the cutting device for a tube glass according to the present
invention, the cut surface with satisfactory quality can be
obtained, and the generation of glass powder can be prevented, in
spite of the fact that the tube glass is cut at a high speed. Thus,
the back-end steps with respect to the tube glass after being cut
can be reduced to increase productivity.
[0040] Further, as described above, with the method of
manufacturing a tube glass product according to the present
invention, the cut surface with satisfactory quality can be
obtained, and the generation of glass powder can be prevented, in
spite of the fact that the tube glass is cut at a high speed. Thus,
the back-end steps with respect to the tube glass after being cut
can be reduced to increase productivity.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1 is a side view of a manufacturing apparatus for a
tube glass product of a first embodiment of the present
invention.
[0042] FIG. 2 is a plan view of a main portion of the manufacturing
apparatus illustrated in FIG. 1.
[0043] FIG. 3 is an enlarged perspective view of a main portion of
a continuous tube glass for illustrating an irradiation mode of
laser light.
[0044] FIG. 4 is an enlarged plan view of a main portion of the
continuous tube glass for illustrating the irradiation mode of
laser light.
[0045] FIG. 5 is a sectional view of a main portion of the
continuous tube glass immediately after an inner crack region is
formed.
[0046] FIG. 6 is a sectional view of a main portion of the
continuous tube glass immediately after cracks in the inner crack
region start propagating in a circumferential direction of the
continuous tube glass.
[0047] FIG. 7 is a sectional view of a main portion of the
continuous tube glass for illustrating a state in which the cracks
in the inner crack region are in the process of propagating in the
circumferential direction of the continuous tube glass.
[0048] FIG. 8 is a front view of an end surface of the continuous
tube glass, for illustrating a state after the cracks in the inner
crack region propagate throughout an entire circumference of the
continuous tube glass.
[0049] FIG. 9 is a plan view of a main portion of the manufacturing
apparatus illustrated in FIG. 1 for illustrating a state
immediately after the continuous tube glass is cut.
[0050] FIG. 10 is a perspective view of a main portion of a tube
glass for illustrating a method of cutting a tube glass according
to a second embodiment of the present invention.
[0051] FIG. 11 is a plan view of a main portion of a manufacturing
apparatus for a tube glass product according to the second
embodiment of the present invention.
[0052] FIG. 12 is a perspective view of a main portion of a tube
glass for illustrating a method of cutting a tube glass according
to a third embodiment of the present invention.
[0053] FIG. 13 is a sectional view of a main portion of a
continuous tube glass immediately after an inner crack region is
formed in an irradiation mode illustrated in FIG. 12.
[0054] FIG. 14 is an enlarged view of a portion A of FIG. 13.
[0055] FIG. 15 is an enlarged view of a main portion of the
continuous tube glass illustrated in FIG. 14 when viewed from a
direction of the arrow B.
[0056] FIG. 16A is an enlarged view of the portion A for
illustrating a process in which cracks in an inner crack region
propagate to an outer peripheral surface of the continuous tube
glass.
[0057] FIG. 16B is an enlarged view of the portion A for
illustrating the case in which the cracks in the inner crack region
propagate to the outer peripheral surface of the continuous tube
glass.
[0058] FIG. 16C is an enlarged view of the portion A for
illustrating the case in which the cracks in the inner crack region
propagate to the outer peripheral surface of the continuous tube
glass.
[0059] FIG. 17 is a sectional view of a main portion of the
continuous tube glass immediately after the cracks in the inner
crack region start propagating in a circumferential direction of
the continuous tube glass.
[0060] FIG. 18 is a sectional view of a main portion of a tube
glass for illustrating a first modification example of the inner
crack region of the present invention.
[0061] FIG. 19 is a sectional view of a main portion of a tube
glass for illustrating a second modification example of the inner
crack region of the present invention.
[0062] FIG. 20 is a sectional view of a main portion of a tube
glass for illustrating a third modification example of the inner
crack region of the present invention.
DESCRIPTION OF EMBODIMENTS
[0063] Now, a first embodiment of the present invention is
described with reference to FIG. 1 to FIG. 9. In the first
embodiment, as an example, description is given below of the case
in which a continuous tube glass is used as a tube glass to be cut,
and the continuous tube glass is cut while being conveyed, to
thereby provide a tube glass product having a predetermined
length.
[0064] FIG. 1 is a view for illustrating an overall configuration
of a manufacturing apparatus 10 for a tube glass product of the
first embodiment of the present invention. The manufacturing
apparatus 10 for a tube glass product illustrated in FIG. 1 is
configured to form a continuous tube glass G1 by a Danner method,
and mainly comprises a glass melting furnace 11, a sleeve 12, a
drive device 13 configured to drive the sleeve 12 to rotate, a
muffle furnace 14 configured to accommodate the sleeve 12, an
annealer 15, a tube drawing device 16 configured to subject the
continuous tube glass G1 to tube drawing forming, a cutting device
17 configured to cut the continuous tube glass G1, and a conveyer
18 configured to convey a tube glass product G2 obtained by cutting
the continuous tube glass G1. The configuration up to a stage in
which the continuous tube glass G1 reaches the cutting device 17 is
first described below.
[0065] A XYZ coordinate system illustrated in FIG. 1 is a
coordinate system on a fixed side. In the first embodiment, a plane
comprising an X-axis and a Y-axis is defined as a horizontal plane,
and a direction along a Z-axis is defined as a vertical direction
(the positive side of the Z-axis is defined as a top, and the
negative side thereof is defined as a bottom). Further, a xyz
coordinate system illustrated in FIG. 3 is a coordinate system on a
moving side (coordinate system on the continuous tube glass G1). In
the same manner as in the XYZ system illustrated in, for example,
FIG. 1, a plane comprising an x-axis and a y-axis is defined as a
horizontal plane, and a direction along a z-axis is defined as a
vertical direction.
[0066] The glass melting furnace 11 is configured to melt a glass
raw material to generate a molten glass M. The molten glass M
generated in the glass melting furnace 11 is supplied to the sleeve
12 in the muffle furnace 14.
[0067] The sleeve 12 is formed into a cylindrical shape through use
of a refractory. In the first embodiment, the sleeve 12 is
partially tapered, and is arranged so that a small-diameter-side
end portion 12a of a tapered portion is directed obliquely
downwardly. The sleeve 12 is connected to the drive device 13
through intermediation of a shaft 19. When the sleeve 12 is driven
to rotate by the drive device 13, the molten glass M supplied to
the sleeve 12 can be wound into a cylindrical shape and be
pultruded into a tube shape from the small-diameter-side end
portion 12a.
[0068] As described above, the molten glass M pultruded into a tube
shape is continuously pulled out of the muffle furnace 14 as the
continuous tube glass G1 and guided into the annealer 15.
[0069] The tube drawing device 16 is arranged on a downstream side
of the annealer 15 and is configured to pull the continuous tube
glass G1 having passed through the annealer 15 at a constant speed
so that the continuous tube glass G1 can be conveyed to the cutting
device 17. Specifically, the continuous tube glass G1 aligned to a
predetermined outer diameter can be supplied to the cutting device
17 by pulling the continuous tube glass G1 in a downstream
direction while sandwiching an upper portion and a lower portion of
the continuous tube glass G1 between a pair of conveyance belts
(not shown), to thereby subject the continuous tube glass G1 to
tube drawing.
[0070] Next, the detail of the cutting device 17 is described with
reference to, for example, FIG. 2.
[0071] As illustrated in FIG. 2, the cutting device 17 is
configured to cut the continuous tube glass G1 to obtain the tube
glass product G2 having a predetermined length. The cutting device
17 comprises an inner crack region forming device 20 configured to
form an inner crack region C1 in a portion of the continuous tube
glass G1 in a circumferential direction thereof and a crack
propagation device 21 configured to generate, in the continuous
tube glass G1, a stress that urges cracks in the inner crack region
C1 to propagate, to thereby cause the cracks to propagate
throughout an entire circumference.
[0072] The inner crack region forming device 20 comprises a laser
oscillator 22 capable of oscillating predetermined laser light (for
example, a pulse laser) L and an optical system 23 configured to
cause the laser light L oscillated from the laser oscillator 22 to
be condensed and enter an inside of the continuous tube glass G1.
In addition, in the first embodiment, the inner crack region
forming device 20 further comprises a scanning portion 24 that is
arranged on a path of the optical system 23 and configured to cause
the laser light L to perform scanning in a predetermined mode as
illustrated in FIG. 3 and a focal point adjusting portion 25
capable of adjusting a position of a focal point F of the laser
light L in the continuous tube glass G1 similarly as illustrated in
FIG. 3.
[0073] In the first embodiment, the optical system 23 comprises a
plurality of mirrors 26 and an objective lens 27 configured to
condense the laser light L transmitted through the plurality of
mirrors 26 into the continuous tube glass G1.
[0074] The scanning portion 24 is formed of a Galvano mirror, for
example, as illustrated in FIG. 2. The scanning portion 24 is
constructed so as to cause the laser light L reflected from the
mirrors 26 to perform scanning in a predetermined locus. For
example, in the first embodiment, as illustrated in FIG. 3, the
scanning portion 24 is constructed so as to cause the laser light L
to perform scanning linearly along the circumferential direction of
the continuous tube glass G1 in such a manner that the focal point
F is included in an imaginary cross section X2 orthogonal to a
center line X1 of the continuous tube glass G1. The scanning locus
described above has a form in the case of being viewed in the
coordinate system (xyz coordinate system illustrated in FIG. 3)
based on the moving continuous tube glass G1. When the scanning
locus is viewed in the coordinate system based on the fixed side,
as illustrated in FIG. 4, the scanning form of the focal point F is
set in the following manner. While the continuous tube glass G1
moves by a predetermined distance s in a direction along the center
line X1, the focal point F moves by a distance from the focal point
F to a focal point F' in a direction (Z-direction of FIG. 3) along
the circumferential direction and moves by the same distance as the
moving distance (predetermined distance s) of the continuous tube
glass G1 in the direction along the center line X1.
[0075] The focal point adjusting portion 25 comprises, for example,
a spatial phase modulator. In this case, specifically, a spatial
phase distribution of the laser light L is set to be able to be
modulated so that the position of the focal point F (more exactly,
the position of the continuous tube glass G1 in a thickness
direction thereof) is adjusted with a phase hologram produced in
advance in accordance with the irradiation direction of the laser
light L controlled by the scanning portion 24. In the first
embodiment, as illustrated in FIG. 3, the position of the focal
point F of the laser light L is adjusted so that the focal point F
is positioned along the circumferential direction of the continuous
tube glass G1 on an outer periphery side (side close to an outer
peripheral surface G1a) of the continuous tube glass G1 in the
thickness direction thereof.
[0076] In the first embodiment, as illustrated in FIG. 2, the crack
propagation device 21 comprises a tensile force applying portion 28
configured to apply a tensile force f1 in the direction along the
center line X1 of the continuous tube glass G1 and a bending force
applying portion 29 configured to apply a bending force f2 to the
continuous tube glass G1 so that the center line X1 of the
continuous tube glass G1 is curved at a predetermined
curvature.
[0077] In this case, for example, the tensile force applying
portion 28 comprises a gripping portion 30 configured to grip a
downstream-side end portion of the continuous tube glass G1 and a
slide drive portion 31 configured to move the gripping portion 30
in the direction along the center line X1. The slide drive portion
31 may be constructed so as to move the gripping portion 30 in
synchronization with the continuous tube glass G1. In this case,
the state in which the tensile force f1 is applied to the
continuous tube glass G1 that is being moved along the center line
X1 can be maintained for a predetermined time period (predetermined
distance).
[0078] Further, the bending force applying portion 29 comprises a
plurality of rollers 32 configured to hold both sides of the
continuous tube glass G1 in a horizontal direction thereof. The
positions of the continuous tube glass G1 supported (held) by the
plurality of rollers 32 are set so that the center line X1 of the
continuous tube glass G1 is curved at a predetermined curvature as
the center line X1 is directed to the downstream side.
[0079] Next, an example of a method of cutting the continuous tube
glass G1 through use of the cutting device 17 having the
above-mentioned configuration is mainly described with reference to
FIG. 2 to FIG. 9.
[0080] First, as illustrated in FIG. 2, the continuous tube glass
G1 sent from the tube drawing device 16 is conveyed further to the
downstream side while being supported by support portions 33 (see
FIG. 1) from below. In this case, the cutting device 17 configured
to cut the continuous tube glass G1 to a predetermined length is
arranged on a downstream side of the tube drawing device 16. When
the downstream-side end portion of the continuous tube glass G1
reaches a predetermined position (or a position immediately before
the predetermined position), the downstream-side end portion of the
continuous tube glass G1 is gripped with the gripping portion 30,
and the gripping portion 30 is moved by the slide drive portion 31
toward the downstream side in a longitudinal direction. Then, the
tensile force f1 in the direction along the center line X1 is
applied to the continuous tube glass G1. Further, the plurality of
rollers 32 forming the bending force applying portion 29 are
arranged on an upstream side of the gripping portion 30, and the
predetermined bending force f2 is applied to the continuous tube
glass G1 having passed between the plurality of rollers 32 so that
the center line X1 is curved at a predetermined curvature. In the
first embodiment, the continuous tube glass G1 is curved at a
predetermined curvature so that the irradiation side (upper right
side of FIG. 2) of the laser light L described later becomes
convex. With this, in the above-mentioned state, the tensile stress
in directions separated from each other along the center line X1 is
generated throughout the entire circumference of the continuous
tube glass G1. In particular, on a large-diameter side of the
curved portion of the continuous tube glass G1, the tensile stress
in the directions separated from each other along the center line
X1 is dominantly distributed.
[0081] Then, the inside of the continuous tube glass G1 is
irradiated with the laser light L under a state in which the
above-mentioned stress distribution is maintained. In this case,
the inner crack region C1 including one or a plurality of cracks is
formed through multiphoton absorption of the laser light L in the
region irradiated with the laser light L by adjusting the
irradiation condition (for example, a pulse width and an output) of
the laser light L. Further, in this case, the laser light L is
caused to perform scanning in a predetermined locus (for example, a
region from the focal point F to the focal point F' of FIG. 3) with
the scanning portion 24, and the position of the focal point F of
the laser light L is changed with the passage of time with the
focal point adjusting portion 25. With this, the focal point F is
moved along the circumferential direction at a predetermined
position of the continuous tube glass G1 in the thickness direction
thereof, to thereby form the inner crack region C1 having a
predetermined circumferential dimension (see FIG. 5). In the
example illustrated in FIG. 5, the inner crack region C1 having a
band shape is formed around the center line X1 within a range of
45.degree. or more and less than 90.degree..
[0082] The cracks in the inner crack region C1 are caused to
propagate in the circumferential direction to cut the continuous
tube glass G1. In the first embodiment, the predetermined stress is
generated in the continuous tube glass G1 at a time of irradiation
with the laser light L. Therefore, when the inner crack region C1
is formed as described above, the cracks naturally propagate in
directions separated from each other along the circumferential
direction from both circumferential end portions of the inner crack
region C1, and a crack propagation region C2 is enlarged along the
circumferential direction (see FIG. 6).
[0083] In this case, when the above-mentioned stress is applied to
the continuous tube glass G1 with the crack propagation device 21
(tensile force applying portion 28 and bending force applying
portion 29), the crack propagation region C2 starts being enlarged
in the directions separated from each other from both the
circumferential sides of the inner crack region C1 (FIG. 6), and
after that, also continues to be enlarged at the same speed along
the circumferential direction (see FIG. 7). As described above, the
cracks continue to propagate (the crack propagation region C2 is
enlarged) in a so-called symmetric manner, with the result that the
right and left crack propagation regions C2 simultaneously reach a
predetermined circumferential position (for example, a position
directly facing a circumferential center position of the inner
crack region C1 with the center line X1 interposed therebetween in
FIG. 8). As a result, the cracks in the inner crack region C1
propagate throughout the entire circumference to cut the continuous
tube glass G1. Further, through this cutting, the tube glass
product G2 having a predetermined length is obtained (see FIG.
9).
[0084] As described above, with the method of manufacturing the
tube glass product G2 and the manufacturing apparatus 10 for the
tube glass product G2 (the method of cutting the continuous tube
glass G1 and the cutting device 17) according to the present
invention, the cracks (inner crack region C1) can be formed in the
continuous tube glass G1 instead of being formed on the surface
thereof, and hence the situation in which glass powder similar to
scratches is generated can be avoided during formation of the
cracks (cracks in the inner crack region C1). Therefore, the time
and labor for removing the glass powder by cleaning can be omitted
to reduce the number of required processes. Further, when the
stress that urges the cracks in the inner crack region C1 to
propagate in the circumferential direction of the continuous tube
glass G1 is generated in the continuous tube glass G1, to thereby
cause the cracks to propagate throughout the entire circumference
of the continuous tube glass G1, the entire region of the cut
surface generated in the continuous tube glass G1 or the tube glass
product G2 can be formed of fracture surfaces of the cracks in the
inner crack region C1 formed through multiphoton absorption of the
laser light L and fracture surfaces of the cracks that propagate
from the inner crack region C1. With this, the occurrence of
cracking and chipping in the cut surface can be prevented to the
extent possible to stably control the properties of the cut
surface, with the result that the cut surface with satisfactory
properties can be obtained. Further, as described above, when the
inner crack region C1 is formed in the portion of the continuous
tube glass G1 in the circumferential direction thereof with the
laser light L, and the cracks in the inner crack region C1 are
caused to propagate in the circumferential direction of the
continuous tube glass G1, a time period required for cutting
becomes shorter as compared to the case in which the inner crack
region C1 is formed throughout the entire circumference by
irradiation with laser light L. Accordingly, the continuous tube
glass G1 can be cut at a high speed, and the manufacturing speed
can be increased.
[0085] Further, in the first embodiment, the continuous tube glass
G1 is irradiated with the laser light L having the focal point F
adjusted to the inside of the continuous tube glass G1 under a
state in which the stress that urges the cracks in the inner crack
region C1 to propagate in the circumferential direction of the
continuous tube glass G1 is generated in the continuous tube glass
G1, to thereby form the inner crack region C1 in the portion of the
continuous tube glass G1 in the circumferential direction thereof.
With this method, a stress distribution state that occurs in the
continuous tube glass G1 can be more accurately reproduced as
compared to, for example, the case in which the above-mentioned
stress is generated immediately after the formation of the inner
crack region C1. Further, the state in which the stress is
generated is maintained more easily when the stress is generated in
the continuous tube glass G1 by applying an external force (tensile
force f1 and bending force f2) to the continuous tube glass G1 in
advance. Thus, the cracks are caused to propagate accurately along
a desired direction, thereby being capable of stably providing the
cut surface with satisfactory quality (surface properties), which
is formed in the inner crack region C1 and the crack propagation
region C2.
[0086] One embodiment (first embodiment) of the method of
manufacturing a continuous tube glass and the manufacturing
apparatus 10 for a continuous tube glass according to the present
invention are described above. However, needless to say, the
manufacturing method and the manufacturing apparatus 10 may adopt
any mode within the scope of the present invention.
[0087] In the above-mentioned embodiment, for example, the case is
illustrated in which the scanning portion 24 is arranged in the
inner crack region forming device 20, and the continuous tube glass
G1 is irradiated with the laser light L while the laser light L
performs scanning in a predetermined locus. However, needless to
say, other irradiation modes may also be adopted. FIG. 10 is a view
for illustrating an irradiation mode of the laser light L according
to one example of the other irradiation modes (second embodiment of
the present invention). In a cutting method according to the second
embodiment, as illustrated in FIG. 10, the inner crack region C1
having a predetermined size is formed by simultaneously irradiating
the continuous tube glass G1 with a plurality of laser lights L1,
L2, . . . Ln instead of causing the laser light L to perform
scanning in a predetermined locus with the scanning portion 24.
[0088] In this case, as illustrated in FIG. 11, the scanning
portion 24 is not required and hence can be omitted. Further, when
the focal point adjusting portion 25 is formed of a spatial phase
modulator, through change in setting of a phase hologram, the
positions of focal points F1, F2, . . . Fn of the laser lights L1,
L2, . . . Ln can be adjusted individually and independently, and
one laser light L can also be dispersed into a desired number of
laser lights. Thus, even when one laser oscillator 22 is used as
illustrated in FIG. 11, predetermined inner positions of the
continuous tube glass G1 can be simultaneously irradiated with a
desired number of the laser lights L1, L2, . . . Ln having the
focal points F1, F2, . . . Fn adjusted to the predetermined inner
positions. When a plurality of points are simultaneously irradiated
with the dispersed laser light L as described above, the inner
crack region C1 of the continuous tube glass G1 can be formed
through one or a significantly small number of (at most several
times) of irradiations, and hence the continuous tube glass G1 can
be cut within a significantly short time period. Thus, the cutting
device 17 according to the present invention can be relatively
easily introduced into a manufacturing line.
[0089] Needless to say, when the scanning portion 24 and the focal
point adjusting portion 25 are used together, scanning can be
performed at a high speed. Therefore, the number of irradiations of
the laser light L can be increased, for example, through a scanning
mode in which the laser light L reciprocates between the focal
points F and F' illustrated in FIG. 3 a plurality of times
(including the range of from several times to hundreds of times).
As the number of irradiations is larger, the irradiation energy per
irradiation can be decreased, and hence the inner crack region C1
having a smaller variation in shape precision can be formed
correspondingly. Needless to say, even when a plurality of points
(focal points F1, F2, . . . Fn) are irradiated with the laser
lights L1, L2, . . . Ln as described above, the inner crack region
C1 may be formed by a plurality of times of irradiations. As the
laser light L that can be used in the case of forming the inner
crack region C1 by one multiple-point irradiation as described
above, there may be given a subnanosecond pulse laser having
relatively large irradiation energy, and as the laser light L that
can be used in the case of forming the inner crack region C1
through scanning involving a plurality of times of reciprocations,
there may be given a picosecond pulse laser having relatively small
irradiation energy.
[0090] Now, a third embodiment of the present invention is
described with reference to FIG. 12 to FIG. 17.
[0091] FIG. 12 is a perspective view of a main portion of the
continuous tube glass G1 for illustrating a method of cutting a
tube glass according to the third embodiment of the present
invention. In the third embodiment, laser light Li (i=1, 2, . . .
n) is irradiated toward a point at which the center line X1 of the
continuous tube glass G1 and the imaginary cross section X2 cross
each other, that is, a center point X10 of the continuous tube
glass G1 on the imaginary cross section X2, and with this, the
inner crack region C1 is formed in a portion of the continuous tube
glass G1 in the circumferential direction thereof at a position
that is significantly close to the outer peripheral surface G1a.
The laser light Li used in this case is a pulse laser, and the
laser light Li is caused to perform scanning, for example, so that
the position of a focal point Fi (i=1, 2, . . . h) of the laser
light Li draws a locus (arc shape with the center point X10 being
the center in this case) illustrated in FIG. 12 through use of the
scanning portion 24 and the focal point adjusting portion 25
illustrated in FIG. 2. When the laser light Li serving as a pulse
laser is caused to perform scanning, a region between the focal
point F1 and the focal point Fn is intermittently irradiated with
the laser light Li, with the result that a plurality of holes H and
a primary crack propagation region C21 described later, which are
generated through abrasion, can be formed.
[0092] In this case, as illustrated in FIG. 13 in an enlarged
state, the inner crack region C1 is formed in the vicinity of the
outer peripheral surface G1a while a surface layer portion G1c
including the outer peripheral surface G1a of the continuous tube
glass G1 is left. Further, in a portion of the surface layer
portion G1c in the circumferential direction thereof, which is to
be a region between the inner crack region C1 and the outer
peripheral surface G1a, the primary crack propagation region C21
formed by propagation of the cracks in the inner crack region C1 to
the outer peripheral surface G1a of the continuous tube glass G1 is
formed.
[0093] As illustrated in FIG. 14 in which a portion A of FIG. 13 is
further enlarged, the plurality of holes H (Hi: i=1, 2, . . . n)
opened to the outer peripheral surface G1a of the continuous tube
glass G1 are formed in the surface layer portion G1c so as to be
adjacent to each other in the circumferential direction. The
plurality of holes H are formed by generating abrasion in the
surface layer portion G1c by irradiation with the pulse laser
(laser light Li) directed to the center point X10 of the continuous
tube glass G1 and extend in the irradiation direction of the laser
light L, that is, in the thickness direction of the tube glass G1.
The primary crack propagation region C21 is formed between the
plurality of holes H adjacent to each other in the circumferential
direction. In the third embodiment, the plurality of holes H and
the primary crack region C21 are formed throughout the entire
region of the surface layer portion G1c in the thickness direction
thereof. In this case, as illustrated in FIG. 15, the primary crack
propagation region C21 connects the plurality of holes H to each
other with the shortest distance (that is, linearly) and is formed
on the outer peripheral surface G1a of the continuous tube glass
G1.
[0094] Here, it is appropriate that a thickness t of the surface
layer portion G1c be set to, for example, 20 .mu.m or less,
preferably 10 .mu.m or less. When the thickness t is set to 20
.mu.m or less, it is possible to expect the action in which the
cracks in the inner crack region C1 propagate to the outer
peripheral surface G1a smoothly and accurately.
[0095] Further, it is appropriate that a circumferential pitch p of
the plurality of holes H be set to, for example, 1.5 times or more
and 5.0 times or less, preferably 2.0 times or more and 4.0 times
or less, in relation to an inner diameter d of the holes H. When
the circumferential pitch p of the plurality of holes H is set
within the above-mentioned range at a magnification with respect to
the inner diameter d of each of the holes H, it is possible to
expect the action in which the cracks propagate smoothly and
accurately so as to connect the plurality of holes H adjacent to
each other in the circumferential direction (see FIG. 15).
[0096] Next, an example of a forming mode of the primary crack
propagation region C21 is described with reference to FIG. 16A to
FIG. 16C.
[0097] First, the following case is considered in which holes Hi-1
are formed in the surface layer portion G1c and the inner crack
region C1 is formed up to a region immediately below the surface
layer portion G1c, for example, as illustrated in FIG. 16A, when
the inside of the continuous tube glass G1 is intermittently
irradiated with the laser light Li serving as the pulse laser while
the laser light Li is caused to perform scanning in a predetermined
direction as described above. In this case, a new inner crack
region C1i is formed (see FIG. 16B) with the laser light Li
subsequently irradiated toward the continuous tube glass G1 through
multiphoton absorption of the laser light Li in a portion adjacent
to the inner crack region C1 (FIG. 16A) that has been formed
immediately below the surface layer portion G1c. Further, in this
case, abrasion of the laser light Li is generated between the new
inner crack region C1i and the outer peripheral surface G1a to form
new holes Hi at corresponding positions of the surface layer
portion G1c.
[0098] Further, substantially at the same time with the formation
of the holes Hi (or after a significantly short time period shorter
than the interval of the irradiation time of the laser light Li),
the cracks in the newly formed inner crack region C1i propagate to
between the holes Hi and Hi-1 in the surface layer portion G1c so
as to connect the newly formed hole Hi and the hole Hi-1 adjacent
to the hole Hi to each other (FIG. 16B). As a result, a primary
crack propagation region C21i is formed between the holes Hi and
Hi-1 adjacent to each other in the circumferential direction, and
the end portion thereof reaches the outer peripheral surface G1a
(see FIG. 16C).
[0099] When laser lights Li+1, . . . Ln are irradiated
intermittently at a predetermined pitch and a predetermined time
interval as described above, new inner crack region C1i+1, . . .
C1n, holes Hi+1, . . . Hn, and primary crack propagation regions
C21i+1, . . . C21n are continuously formed successively, and
finally, the inner crack region C1 and the primary crack
propagation region C21 illustrated in FIG. 13 are formed.
[0100] Then, as illustrated in FIG. 17, the cracks in the inner
crack region C1 or the cracks in the inner crack region C1 and the
cracks in the primary crack propagation region C21 are caused to
propagate in the circumferential direction. Also in the third
embodiment, when a predetermined stress is generated in the
continuous tube glass G1 at a time of irradiation with the laser
light L1 in the same manner as in the first embodiment, the cracks
naturally propagate in the directions separated from each other
along the circumferential direction from both the circumferential
end portions of the inner crack region C1, and the crack
propagation region (secondary crack propagation region C22 in this
case) is enlarged along the circumferential direction, by forming
the inner crack region C1 and the primary crack propagation region
C21 as described above. As a result, the continuous tube glass G1
is cut throughout the entire circumference thereof. Further,
through this cutting, the tube glass product G2 having a
predetermined length is obtained in the same manner as in, for
example, FIG. 9.
[0101] As described above, also with the method of cutting a tube
glass according to the third embodiment of the present invention,
an initial crack (inner crack region C1) can be formed in the
continuous tube glass G1, and hence the situation in which glass
powder is generated can be avoided. Further, the cut surface with
satisfactory properties can be obtained by generating a stress that
urges the cracks in the inner crack region C1 to propagate in the
circumferential direction of the continuous tube glass G1 to cause
the cracks to propagate throughout the entire circumference of the
continuous tube glass G1. In particular, when the inner crack
region C1 is formed in the vicinity of the outer peripheral surface
G1a while the surface layer portion G1c including the outer
peripheral surface G1a of the continuous tube glass G1 is left, the
cracks in the inner crack region C1 are caused to propagate to the
outer peripheral surface G1a (FIG. 16A to FIG. 16C), and the cracks
are caused to propagate throughout the entire circumference of the
continuous tube glass G1 with the stress that urges the cracks to
propagate in the circumferential direction of the continuous tube
glass G1 as in the third embodiment, the stress required for
cutting the entire circumference of the continuous tube glass G1
can be reduced. Thus, the cut surface with even more satisfactory
properties can be obtained.
[0102] Further, in the third embodiment, abrasion is generated in
the surface layer portion G1c of the continuous tube glass G1 to
form the plurality of holes H extending in the irradiation
direction of the laser light Li by irradiation with the laser light
Li, and the circumferential pitch p between the plurality of holes
H is adjusted, to thereby cause the cracks in the inner crack
region C1 to propagate to the outer peripheral surface G1a so as to
connect the plurality of holes H to each other (FIG. 15). When the
plurality of holes H are formed through abrasion of the laser light
Li in the surface layer portion G1c of the continuous tube glass
G1, and the circumferential pitch p of the plurality of holes H is
adjusted to an appropriate size, the primary crack propagation
region C21 can be formed stably. Thus, the cracks can be caused to
accurately propagate to the outer peripheral surface G1a to provide
the cut surface with satisfactory and stable properties.
[0103] In the third embodiment, the case is illustrated in which
the cracks in the inner crack region C1 are caused to propagate to
the outer peripheral surface G1a so as to connect the plurality of
holes H to each other by generating abrasion in the surface layer
portion G1c of the continuous tube glass G1 to form the plurality
of holes H extending in the irradiation direction of the laser
light Li by irradiation with the laser light Li. However, needless
to say, the present invention is not limited thereto. That is, even
when the plurality of holes H are not formed in the surface layer
portion G1c through abrasion, any specific means may be used as
long as the cracks in the inner crack region C1 can be caused to
propagate to the outer peripheral surface G1a.
[0104] Further, in the first to third embodiments, the case is
described in which the spatial phase modulator is used as the focal
point adjusting portion 25, but needless to say, other devices may
also be used as the focal point adjusting portion 25. Known optical
devices having a focal point adjusting function such as an aspheric
lens and various diffraction gratings typified by, for example, a
F.theta. lens, may be used.
[0105] Further, in the first to third embodiments, the case is
illustrated in which the inner crack region C1 is formed on the
outer periphery side (side close to the outer peripheral surface
G1a) of the continuous tube glass G1 in the thickness direction
thereof, but needless to say, other modes may also be adopted. FIG.
18 is a sectional view of an inner crack region C3 of one example
of the other modes (first modification example). As illustrated in
FIG. 18, the inner crack region C3 is formed on a side closer to
the inner peripheral surface G1b with respect to the center
position of the continuous tube glass G1 in the thickness direction
thereof. Even when the inner crack region C3 is formed at such
position, the cracks in the inner crack region C3 can be caused to
propagate throughout the entire circumference of the continuous
tube glass G1 to cut the continuous tube glass G1 by generating an
appropriate stress in the continuous tube glass G1.
[0106] Further, in the first to third embodiments, the case is
illustrated in which, as the inner crack regions C1 and C3, the
inner crack regions having a constant dimension in the thickness
direction (dimension in a direction along a radial direction of the
continuous tube glass G1) are formed, but needless to say, other
modes may also be adopted. FIG. 19 is a sectional view of an inner
crack region C4 according to one example of the other modes (second
modification example). As illustrated in FIG. 19, in the inner
crack region C4, a large-diameter side C41 (side close to the outer
peripheral surface G1a of the continuous tube glass G1) is formed
into a substantially arc shape in conformity with the outer
peripheral surface G1a, and a radially inner side C42 (side close
to the inner peripheral surface G1b of the continuous tube glass
G1) is formed into a substantially linear shape. Thus, the
dimension of the inner crack region C4 in the thickness direction
thereof is reduced from the circumferential center to both
circumferential ends. Even when the inner crack region C4 is formed
at such position, the cracks in the inner crack region C4 can be
caused to propagate throughout the entire circumference of the
continuous tube glass G1 to cut the continuous tube glass G1 by
generating an appropriate stress in the continuous tube glass
G1.
[0107] Further, in the first to third embodiments, the case is
illustrated in which the inner crack regions C1, C3, and C4 are
each formed into a shape in conformity with the outer peripheral
surface G1a of the continuous tube glass G1 as a whole, but
needless to say, the inner crack regions C1, C3, and C4 may also be
formed into other shapes. FIG. 20 is a sectional view of an inner
crack region C5 of one example of the other modes (third
modification example). As illustrated in FIG. 20, in the inner
crack region C5, a radially outer side C51 and a radially inner
side C52 are each formed into a substantially linear shape.
Further, in the illustrated example, the radially outer side C51
and the radially inner side C52 extend in a direction orthogonal to
the radial direction of the continuous tube glass G1. Even when the
continuous tube glass G1 is formed into a constant shape
irrespective of the shape, the cracks in the inner crack region C5
can be caused to propagate throughout the entire circumference of
the continuous tube glass G1 to cut the continuous tube glass G1 by
generating an appropriate stress in the continuous tube glass
G1.
[0108] Further, in the first to third embodiments, the case is
illustrated in which the number of each of the inner crack regions
C1 and C3 to C5 to be formed in the continuous tube glass G1 is set
to one, but needless to say, the present invention is not limited
to those embodiments. Any number of the inner crack regions may be
formed as long as the inner crack regions are formed in the
continuous tube glass G1 to be cut. Although not shown, for
example, the following may be performed. Two portions opposed to
each other with the center line X1 interposed therebetween are
irradiated with the laser light L to form the inner crack regions
C1 in the above-mentioned two portions, and the cracks are caused
to propagate (the crack propagation region C2 or the secondary
crack propagation region C22 is enlarged) in the directions
separated from each other from both circumferential ends of each of
the inner crack regions C1 to cause the cracks to propagate
throughout the entire circumference of the continuous tube glass
G1.
[0109] Alternatively, although not shown, the following may also be
performed. A plurality of dot-like inner crack regions are formed
at constant intervals in the circumferential direction or the
radial direction, and the cracks in each of the inner crack regions
are caused to propagate so as to connect each of the inner crack
regions to each other. In any case, any shape and number of the
inner crack regions may be adopted as long as the cracks can be
finally caused to propagate throughout the entire circumference of
the continuous tube glass G1.
[0110] Further, in the first to third embodiments, the case is
illustrated in which the position of the focal point F (F1, F2, . .
. Fn) of the laser light L (L1, L2, . . . Ln) is set to a
predetermined position with the focal point adjusting portion 25,
but needless to say, other modes may also be adopted. For example,
although not shown, the following mode may be adopted. An outer
diameter measuring portion configured to measure an outer diameter
of the continuous tube glass G1 is arranged on an upstream side of
the irradiation region of the laser light L in the continuous tube
glass G1, and outer diameter data obtained through measurement with
the outer diameter measuring portion is fed back to the focal point
adjusting portion 25 to finely adjust the position of the focal
point F of the laser light L. With this, even when the outer
diameter of the continuous tube glass G1 changes in accordance with
the elapsed time after the start of tube drawing forming, the inner
crack region C1 can be formed at an appropriate position by
adjusting the position of the focal point F of the laser light L to
be irradiated in accordance with the change.
[0111] Further, in the first to third embodiments, the case is
illustrated in which the tensile force f1 in the direction along
the center line X1 is applied to the continuous tube glass G1 by
gripping the downstream-side end portion of the continuous tube
glass G1 to be cut with the gripping portion 30 and moving the
gripping portion 30 to the downstream side in the longitudinal
direction with the slide drive portion 31, and the predetermined
bending force f2 is applied to the continuous tube glass G1 so that
the center line X1 of the continuous tube glass 1 is curved at a
predetermined curvature by causing the continuous tube glass G1 to
pass between the plurality of rollers 32. However, needless to say,
one or both of the tensile force f1 and the bending force f2 may be
applied to the continuous tube glass G1 with other configurations.
In other words, as long as the stress that urges the cracks in the
inner crack region C1 to propagate in the circumferential direction
of the continuous tube glass G1 can be generated in the continuous
tube glass G1, any application structure of an external force
(tensile force f1 and bending force f2) may be adopted, and there
is no particular limitation on the form of the external force.
[0112] Further, it is not necessarily required to apply an external
force to the continuous tube glass G1 as long as the stress that
urges the cracks in the inner crack region C1 to propagate in the
circumferential direction of the continuous tube glass G1 can be
generated in the continuous tube glass G1. For example, although
not shown, the stress that urges the cracks in the inner crack
region C1 to propagate in the circumferential direction of the
continuous tube glass G1 may be generated by subjecting a portion
of the continuous tube glass G1 in which the inner crack region C1
is to be formed to local heating and cooling.
[0113] Further, in the above-mentioned description, the case is
illustrated in which, the inner crack region C1 is formed in the
portion of the continuous tube glass G1 in the circumferential
direction thereof by irradiating the inside of the continuous tube
glass G1 with the laser light L having the focal point F adjusted
to the inside of the continuous tube glass G1 under a state in
which the stress that urges the cracks in the inner crack region C1
to propagate in the circumferential direction of the continuous
tube glass G1 is generated in the continuous tube glass G1 in
advance. However, needless to say, it is not necessary to limit the
formation of the inner crack region C1 to the above-mentioned
order. The order may be reversed as long as the stress that urges
the cracks in the inner crack region C1 to propagate in the
circumferential direction of the continuous tube glass G1 can be
generated. That is, in the first to third embodiments, the stress
that urges the cracks in the inner crack region C1 to propagate in
the circumferential direction of the continuous tube glass G1 may
be generated in the continuous tube glass G1 after the inner crack
region C1 is formed in the portion of the continuous tube glass G1
in the circumferential direction thereof by irradiation with the
laser light L.
[0114] Further, in the above-mentioned description, the case is
illustrated in which the continuous tube glass G1 illustrated in,
for example, FIG. 1 is targeted for cutting to obtain the tube
glass product G2 through cutting. However, needless to say, even
when other tube glasses are targeted for cutting, the present
invention is applicable. For example, although not shown, even when
a relatively long tube glass that has already been cut (having end
portions on both longitudinal sides) is cut to provide a relatively
short tube glass, the present invention is applicable. Needless to
say, even when the tube glass obtained through cutting is not a
final product, the present invention is applicable.
REFERENCE SIGNS LIST
[0115] 10 manufacturing apparatus [0116] 11 glass melting furnace
[0117] 12 sleeve [0118] 13 drive device [0119] 14 muffle furnace
[0120] 15 annealer [0121] 16 tube drawing device [0122] 17 cutting
device [0123] 18 conveyer [0124] 20 inner crack region forming
device [0125] 21 crack propagation device [0126] 22 laser
oscillator [0127] 23 optical system [0128] 24 scanning portion
[0129] 25 focal point adjusting portion [0130] 27 objective lens
[0131] 28 tensile force applying portion [0132] 29 bending force
applying portion [0133] 30 gripping portion [0134] 31 slide drive
portion [0135] 32 roller [0136] 33 support portion [0137] C1, C3,
C4, C5 inner crack region [0138] C2 crack propagation region [0139]
C21 primary crack propagation region [0140] C22 secondary crack
propagation region [0141] d inner diameter of hole [0142] F, F',
F1, F2, . . . Fn focal point [0143] f1 tensile force [0144] f2
bending force [0145] G1 continuous tube glass [0146] G1a outer
peripheral surface [0147] G1c surface layer portion [0148] G2 tube
glass product [0149] H hole [0150] L, L1, L2, . . . , Ln laser
light [0151] M molten glass [0152] p circumferential pitch of hole
[0153] t thickness of surface layer portion [0154] X1 center line
[0155] X10 center point [0156] X2 imaginary cross section
* * * * *